Allegations that the author of a report on Chatham Rock Phosphate (CRP) signed a Greenpeace petition has led CRP to ask the report be withdrawn.

The demand comes after CRP criticised the content and timing of the Environmental Protection Authority's staff report, which was issued last week.

The report said it could not recommend a marine consent for CRP to vacuum phosphate nodules from the seabed of the Chatham Rise, about 450 kilometres east of Christchurch.

CRP's managing director Chris Castle said a new and potentially more serious basis for concern about the validity of the report and its conclusions had emerged.

"It has come to CRP's attention that one of the key authors of the EPA staff report appears to have been a signatory to a Greenpeace petition in 2010 seeking the Government permanently stop all plans to open up New Zealand's coastal waters to offshore oil drilling and stop any expansion of coal mining in New Zealand," Castle said.

"If this is the case, it raises very serious questions over the objectivity of the report and its conclusions."

EPA chief executive Rob Forlong confirmed it had been advised that the name on the Greenpeace petition corresponded with the name of an EPA staff member who worked on the report.

"The EPA has rigorous processes in place to ensure its work is objective and robust. For example, the staff report had input from many staff, and was extensively peer-reviewed internally before it was released." Forlong said a decision-making committee appointed by the EPA board to hear and decide the application had been informed of the concerns. If there was an issue he would commission an independent peer review of the staff report.

"It is very common for parties to an application to criticise the staff report - whether they are the applicant or a submitter opposing an application.

"The usual way parties address any concerns is through the process of presenting their evidence at a hearing." But Castle considered the report to be potentially biased and therefore totally unreliable. It intended to seek the formal withdrawal of the report.

CRP would shortly apply to the EPA's decision-making committee for that to occur.

"While I accept the subject matter of the petition does not refer directly to offshore mining projects such as ours, there is certainly a strong enough link between the subject matter of the petition and our project to raise an alarm," Castle said.

"This is further compounded by the fact that Greenpeace is a key submitter in opposition to CRP's marine consent application."

Any potential relationship with a submitter needed to be disclosed by EPA staff and, if any connection existed, the staff member should not be involved, he said.

"We have asked the EPA to confirm whether the staff member was a signatory to the petition.

"The EPA's response has been the staff member is not and has never been a financial member of Greenpeace and, while the individual does not recall whether or not they signed the petition, the staff member has conceded it is possible that they may have signed it.

"We understand the staff member did confirm they have, from time to time, received communications from Greenpeace. We have asked the EPA to investigate the matter further, but the EPA advised it is satisfied with the individual's response."

An EPA-appointed decision-making committee will hear CRP's application starting on September 25.

The EPA said a decision was due about December 18, although CRP has consistently said it believed a decision might be possible in November.